1. Field of the invention
The present invention relates, in general, to methods for the formation of device separation film among manufacture processes for a semiconductor device and, more particularly, to methods for forming a field oxide film in the semiconductor device, capable of securing an active region more large and smoothing the surface of the field oxide film.
2. Description of the Prior Art
For better understanding of the background of the present invention, there will be described a conventional method for the formation of device separation film in a semiconductor device along with its problems.
Referring initially to FIG. 1A, there is schematically illustrated the conventional method for forming a field oxide film in a semiconductor device. As shown in this figure, a silicon substrate 1 is covered with a pad oxide film 2, which is subsequently overlaid with a first nitride film 3. An etching process is carried out to open a predetermined portion of the nitride film 3 in which a field oxide film is to be formed, leaving a pattern of the nitride film 3. Thereafter, on the opened portion, there is deposited a second nitride film, which is subsequently subjected to etch back, so as to form a spacer nitride film 6 at either side wall thereof. Using the spacer nitride film 6 and the first nitride film 3 as an etch mask, a trench 7 is formed in the silicon substrate 1.
Now, referring to Fig. 1B, there is a schematic view showing a field oxide film 10 which is formed by applying an oxidation process to the structure resulting from FIG. 1A. While the field oxide film 10 is being formed, oxygens are diffused through the pad oxide film 2, oxidizing a part of the silicon substrate 1. Accordingly, as shown in FIG. 1B, ears C of the field oxide film 10 are generated and bird's beaks form thick in the active region.
These ears and the bird's beaks formed at the-field oxide film 10 not only reduce the area of the active region but also make the surface of the field oxide film rough, causing various difficulties in performing subsequent processes.